Conventionally, in the case of the branching, the leading-in, the connecting or the like of a multi-optical fiber cable, comprising a plurality of optical fibers, a connecting box has been used to hold or contain surplus lengths of connecting end portions of optical fibers.
One conventional connecting box under consideration, shown in FIG. 5, comprises: a pair of opposed tray guides 2 and 2' mounted on a connecting plate 3 and each having vertically spaced shelves, and a plurality of container trays 1 withdrawably supported respectively on the opposed shelves of the two tray guides 2 and 2' in a stacked manner.
For connecting two multi-optical fiber cables A and A' together using this conventional connecting box, the sheaths of the two cables A and A' are first fastened respectively to the opposite ends of the connecting plate 3 by cable holders 4 and 4'. Then, the lowermost tray of the plurality of trays 1 is withdrawn from the tray guides 2 and 2' transversely of the connecting plate 3, and two of the optical fibers a, extending from the sheath end of each of the cables A and A', are introduced into the lowermost tray of the plurality of trays 1. The optical fibers a of the cable A are connected respectively to the optical fibers a of the cable A' at their distal ends by means of connectors 5. A surplus length b of each optical fiber a is formed into a loop and is contained in the lowermost tray. Then, the lowermost tray is pushed back into the tray guides 2 and 2'. Thus, the connecting operation with respect to the lowermost tray 1 is completed. Then, the next lowermost tray of the plurality of trays 1, disposed immediately above the lowermost tray, is withdrawn and the same connecting operation is carried out. The operation continues for any number of optic fibers and any number of trays. In this manner, the connection between the other optical fibers a of the cables A and A' is made according to the same procedure.
With this construction, however, when the tray 1 is pushed into the tray guides 2 and 2', after the connection between the optical fibers a of the multi-optical fiber cables A and A' as well as the formation of the surplus lengths b of optical fibers a into a loop are made in the withdrawn condition of the tray 1, that portion c of each optical fiber a extending between the cable holder 4 and the end of tray 1 becomes loosened or slacked, so that the portion c tends to be formed into a loop having an arcuate portion of a small radius of curvature, as shown in FIG. 6.
The presence of such an arcuate portion of a small radius of curvature in the optical fiber will adversely affect its transmission characteristics.
Another disadvantage of the conventional connecting box is that once the tray 1 is pushed into the tray guides 2 and 2', the surplus lengths of optical fibers contained in the tray cannot easily be inspected.